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General DescriptionThe MAX712/MAX713 fast-charge Nickel Metal Hydride(NiMH) and Nickel Cadmium (NiCd) batteries from a DCsource at least 1.5V higher than the maximum batteryvoltage. 1 to 16 series cells can be charged at rates upto 4C. A voltage-slope detecting analog-to-digital convert-er, timer, and temperature window comparator determinecharge completion. The MAX712/MAX713 are poweredby the DC source via an on-board +5V shunt regulator.They draw a maximum of 5µA from the battery when notcharging. A low-side current-sense resistor allows thebattery charge current to be regulated while still supplying power to the battery’s load.
The MAX712 terminates fast charge by detecting zerovoltage slope, while the MAX713 uses a negative voltage-slope detection scheme. Both parts come in 16-pin DIP and SO packages. An external power PNP tran-sistor, blocking diode, three resistors, and threecapacitors are the only required external components.
The evaluation kit is available: Order the MAX712EVKIT-DIP for quick evaluation of the linear charger.
________________________ApplicationsBattery-Powered Equipment
Laptop, Notebook, and Palmtop ComputersHandy-TerminalsCellular Phones
Portable Consumer ProductsPortable StereosCordless Phones
Features♦ Fast-Charge NiMH or NiCd Batteries♦ Voltage Slope, Temperature, and Timer
Fast-Charge Cutoff♦ Charge 1 to 16 Series Cells♦ Supply Battery’s Load While Charging
(Linear Mode)♦ Fast Charge from C/4 to 4C Rate♦ C/16 Trickle-Charge Rate♦ Automatically Switch from Fast to Trickle Charge♦ Linear Mode Power Control♦ 5µA (max) Drain on Battery when Not Charging♦ 5V Shunt Regulator Powers External Logic
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________________________________________________________________ Maxim Integrated Products 1
MAX712MAX713
THI
R2150Ω
R368kΩ
R422kΩ
R1
10μF
C40.01μF
C11μF
C310μF
C20.01μF
DRV
Q12N6109DC IN
WALL CUBE
D11N4001
BATTERY
RSENSE
V+
VLIMIT BATT+REF
TEMP
BATT- TLO GNDCCLOAD
Typical Operating Circuit
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
REF
V+
DRV
GND
BATT-
CC
PGM3
PGM2
VLIMIT
BATT+
PGM0
PGM1
THI
TLO
TEMP
FASTCHG
TOP VIEW
MAX712MAX713
DIP/SO
Pin Configuration
19-0100; Rev 6; 12/08
PART
MAX712CPE
MAX712CSE
MAX712C/D 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP RANGE PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
Ordering Information
Ordering Information continued at end of data sheet.*Contact factory for dice specifications.**Contact factory for availability and processing to MIL-STD-883.
MAX712EPE
MAX712ESE
MAX712MJE -55°C to +125°C
-40°C to +85°C
-40°C to +85°C 16 Plastic DIP
16 Narrow SO
16 CERDIP**
EVALUATION KIT
AVAILABLE
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,or visit Maxim's website at www.maxim-ic.com.
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2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(IV+ = 10mA, TA = TMIN to TMAX, unless otherwise noted. Refer to the Typical Operating Circuit. All measurements are with respect toBATT-, not GND.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.
V+ to BATT- .................................................................-0.3V, +7VBATT- to GND........................................................................±1VBATT+ to BATT-
Power Not Applied............................................................±20VWith Power Applied ................................The higher of ±20V or
±2V x (programmed cells)DRV to GND ..............................................................-0.3V, +20VFASTCHG to BATT- ...................................................-0.3V, +12VAll Other Pins to GND......................................-0.3V, (V+ + 0.3V)V+ Current.........................................................................100mADRV Current. .....................................................................100mA
REF Current.........................................................................10mAContinuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C............842mWNarrow SO (derate 8.70mW/°C above +70°C .............696mWCERDIP (derate 10.00mW/°C above +70°C ................800mW
Operating Temperature RangesMAX71_C_E .......................................................0°C to +70°CMAX71_E_E .................................................... -40°C to +85°CMAX71_MJE ................................................. -55°C to +125°C
Storage Temperature Range .............................-65°C to +150°CLead Temperature (soldering, 10s) .................................+300°C
VDRV = 10V
V+ = 0V, BATT+ = 17V
PGM3 = BATT-
5mA < IV+ < 20mA
PGM3 = REF
PGM3 = open
PGM3 = V+
0V < TEMP < 2V, TEMP voltage rising
VLIMIT = V+
Per cell
PGM0 = PGM1 = BATT-, BATT+ = 30V
1.2V < VLIMIT < 2.5V, 5mA < IDRV < 20mA,PGM0 = PGM1 = V+
0mA < IREF < 1mA
CONDITIONS
mA30DRV Sink Current
%-1.5 1.5Battery-Voltage to Cell-VoltageDivider Accuracy
%-15 15Timer Accuracy
mV
26.0 31.3 38.0
Trickle-Charge VSENSE12.0 15.6 20.0
4.5 7.8 12.0
1.5 3.9 7.0
mV225 250 275Fast-Charge VSENSE
V1.6 1.65 1.7Internal Cell Voltage Limit
mV-30 30VLIMIT Accuracy
µA-1 1THI, TLO, TEMP, VLIMIT Input Bias Current
µA5BATT+ Leakage
mA5IV+ (Note 1)
V4.5 5.5V+ Voltage
mV-10 10THI, TLO Offset Voltage (Note 2)
V0 2THI, TLO, TEMP Input Range
V1.25 2.50External VLIMIT Input Range
V0.35 0.50Undervoltage Lockout
kΩ30BATT+ Resistance with Power On
µF0.5C1 Capacitance
nF5C2 Capacitance
V1.96 2.04REF Voltage
UNITSMIN TYP MAXPARAMETER
MAX712
MAX713 mV/tAper cell0
Voltage-Slope Sensitivity (Note 3)-2.5
ELECTRICAL CHARACTERISTICS (continued)(IV+ = 10mA, TA = TMIN to TMAX, unless otherwise noted. Refer to the Typical Operating Circuit. All measurements are with respect toBATT-, not GND.)
Note 1: The MAX712/MAX713 are powered from the V+ pin. Since V+ shunt regulates to +5V, R1 must be small enough to allow atleast 5mA of current into the V+ pin.
Note 2: Offset voltage of THI and TLO comparators referred to TEMP.Note 3: tA is the A/D sampling interval (Table 3).Note 4: This specification can be violated when attempting to charge more or fewer cells than the number programmed. To ensure
proper voltage-slope fast-charge termination, the (maximum battery voltage) ÷ (number of cells programmed) must fallwithin the A/D input range.
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Battery voltage ÷ number of cells programmed
VFASTCHG = 10V
VFASTCHG = 0.4V
CONDITIONS
V1.4 1.9A/D Input Range (Note 4)
µA10FASTCHG High Current
mA2FASTCHG Low Current
UNITSMIN TYP MAXPARAMETER
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
20
1k 100k 1M10k 10M
CURRENT-SENSE AMPLIFIERFREQUENCY RESPONSE (with 15pF)
-20
FREQUENCY (Hz)
GAIN
(dB)
PHAS
E (D
EGRE
ES)
-10
0
10
40
-120
-80
-40
0
C2 = 15pFFASTCHG = 0V
VOUTVINCURRENT-
SENSE AMP
BATT-
BATT-
CC
GND
- -
+ +
AV
Φ
MAX712/13 toc0120
-10
-2010 1k
CURRENT-SENSE AMPLIFIERFREQUENCY RESPONSE (with 10nF)
0
10
40
-80
-120
-40
0
FREQUENCY (Hz)
GAIN
(dB)
PHAS
E (D
EGRE
ES)
100 10k
C2 = 10nFFASTCHG = 0V
AV
Φ
MAX712/13 toc02
100
0.11.95 1.97 2.01 2.05
CURRENT ERROR-AMPLIFIERTRANSCONDUCTANCE
1
10
VOLTAGE ON CC PIN (V)
DRV
PIN
SINK
CUR
RENT
(mA)
1.99 2.03
FASTCHG = 0V, V+ = 5V
MAX
712/
13 to
c03 5.8
4.8
0 60
SHUNT-REGULATOR VOLTAGEvs. CURRENT
5.6
CURRENT INTO V+ PIN (mA)
V+ V
OLTA
GE (V
)
30
5.2
5.0
10 20 50
5.4
4.0
4.4
4.2
4.6
40
DRV NOT SINKING CURRENT
DRV SINKING CURRENT
MAX
712/
13 to
c04
1.0
0 60
ALPHA SENSORS PART No. 14A1002STEINHART-HART INTERPOLATION
1.6
BATTERY TEMPERATURE(°C)
TEM
P PI
N VO
LTAG
E (V
)
BATT
ERY
THER
MIS
TOR
RESI
STAN
CE (k
Ω)
30
1.4
1.2
10 20 500.2
0.6
0.4
0.8
20
35
30
25
0
10
5
15
40
MAX712/13 toc05
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4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
90
MAX713NiMH BATTERY CHARGING
CHARACTERISTICS AT C RATE
CHARGE TIME (MINUTES)0 30 60
V
T
MAX712/13 toc07
ΔVΔt CUTOFF
1.60
CELL
VOL
TAGE
(V)
CELL
TEM
PERA
TURE
(°C)
1.45
1.55
1.50
40
25
35
30
150
MAX713NiMH BATTERY CHARGING
CHARACTERISTICS AT C/2 RATE
1.55
1.40
0 50
1.50
1.45
40
25
35
30
V
T
ΔVΔt CUTOFF
CHARGE TIME (MINUTES)
CELL
VOL
TAGE
(V)
CELL
TEM
PERA
TURE
(°C)
100
MAX712/13 toc09
1.40
0
MAX713NiCd BATTERY-CHARGING
CHARACTERISTICS AT C/2 RATE
1.45
CHARGE TIME (MINUTES)
CELL
VOL
TAGE
(V)
CELL
TEM
PERA
TURE
(°C)1.50
25
30
35
50 150100
ΔVΔt CUTOFF
V
T
MAX712/13 toc08
15 20
MAX713CHARGING CHARACTERISTICS OF AFULLY-CHARGED NiMH BATTERY
1.60
CHARGE TIME (MINUTES)
CELL
VOL
TAGE
(V)
CELL
TEM
PERA
TURE
(°C)
1.45
1.65
0 5
1.55
1.50
40
25
35
30
10
V
T
ΔVΔt CUTOFF
5 MINUTE RESTBETWEEN CHARGES
MAX712/13 toc10
1.45
0
MAX713CHARGING CHARACTERISTICS OF A
FULLY CHARGED NiMH BATTERY
1.50
CHARGE TIME (MINUTES)
CELL
VOL
TAGE
(V)
CELL
TEM
PERA
TURE
(°C)
1.60
1.65
1.55
25
30
40
35
5 1510
5-HOUR REST BETWEEN CHARGES
ΔVΔt CUTOFF
V
T
20
MAX712/13 toc11
90
MAX713NiCd BATTERY CHARGING
CHARACTERISTICS AT C RATE
1.55
CHARGE TIME (MINUTES)
CELL
VOL
TAGE
(V)
CELL
TEM
PERA
TURE
(°C)
1.40
0 30
1.50
1.45
40
25
35
30
60
V
T
ΔVΔt CUTOFF
MAX712/13 toc06
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Pin Description
Compensation input for constant current regulation loopCC11
Negative terminal of batteryBATT-12
System ground. The resistor placed between BATT- and GND monitors the current into the battery.GND13
Current sink for driving the external PNP current sourceDRV14
Shunt regulator. The voltage on V+ is regulated to +5V with respect to BATT-, and the shunt currentpowers the MAX712/MAX713.
V+15
Trip point for the under-temperature comparator. If the MAX712/MAX713 power on with the voltage-onTEMP less than TLO, fast charge is inhibited and will not start until TEMP rises above TLO.
TLO6
Sense input for temperature-dependent voltage from thermistors.TEMP7
Open-drain, fast-charge status output. While the MAX712/MAX713 fast charge the battery, FASTCHGsinks current. When charge ends and trickle charge begins, FASTCHG stops sinking current.
FASTCHG8
PGM2 and PGM3 set the maximum time allowed for fast charging. Timeouts from 33 minutes to 264minutes can be set by connecting to any of V+, REF, or BATT-, or by leaving the pin unconnected(Table 3). PGM3 also sets the fast-charge to trickle-charge current ratio (Table 5).
PGM2,PGM3
9, 10
Trip point for the over-temperature comparator. If the voltage-on TEMP rises above THI, fast charge ends.THI5
PGM0 and PGM1 set the number of series cells to be charged. The number of cells can be set from 1 to 16 by connecting PGM0 and PGM1 to any of V+, REF, or BATT-, or by leaving the pin unconnected(Table 2). For cell counts greater than 11, see the Linear-Mode, High Series Cell Count section.Charging more or fewer cells than the number programmed may inhibit ΔV fast-charge termination.
PGM0,PGM1
3, 4
PIN
Positive terminal of batteryBATT+2
Sets the maximum cell voltage. The battery terminal voltage (BATT+ - BATT-) will not exceed VLIMIT x(number of cells). Do not allow VLIMIT to exceed 2.5V. Connect VLIMIT to VREF for normal operation.
VLIMIT1
FUNCTIONNAME
2V reference outputREF16
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Getting StartedThe MAX712/MAX713 are simple to use. A completelinear-mode fast-charge circuit can be designed in afew easy steps. A linear-mode design uses the fewestcomponents and supplies a load while charging.
1) Follow the battery manufacturer’s recommendationson maximum charge currents and charge-terminationmethods for the specific batteries in your application.Table 1 provides general guidelines.
2) Decide on a charge rate (Tables 3 and 5). The slow-est fast-charge rate for the MAX712/MAX713 is C/4,because the maximum fast-charge timeout period is264 minutes. A C/3 rate charges the battery in aboutthree hours. The current in mA required to charge atthis rate is calculated as follows:
IFAST = (capacity of battery in mAh)–––––––––––––––––––––––––
(charge time in hours)
Depending on the battery, charging efficiency can beas low as 80%, so a C/3 fast charge could take 3 hoursand 45 minutes. This reflects the efficiency with whichelectrical energy is converted to chemical energy withinthe battery, and is not the same as the power-conversion efficiency of the MAX712/MAX713.
3) Decide on the number of cells to be charged (Table 2).If your battery stack exceeds 11 cells, see the Linear-Mode High Series Cell Count section. Wheneverchanging the number of cells to be charged, PGM0
and PGM1 must be adjusted accordingly. Attemptingto charge more or fewer cells than the number pro-grammed can disable the voltage-slope fast-chargetermination circuitry. The internal ADC’s input volt-age range is limited to between 1.4V and 1.9V (seethe Electrical Characteristics), and is equal to thevoltage across the battery divided by the number ofcells programmed (using PGM0 and PGM1, as inTable 2). When the ADC’s input voltage falls out ofits specified range, the voltage-slope termination cir-cuitry can be disabled.
4) Choose an external DC power source (e.g., wallcube). Its minimum output voltage (including ripple)must be greater than 6V and at least 1.5V higherthan the maximum battery voltage while charging.This specification is critical because normal fast-charge termination is ensured only if this require-ment is maintained (see Powering theMAX712/MAX713 section for more details).
5) For linear-mode designs, calculate the worst-casepower dissipation of the power PNP and diode (Q1and D1 in the Typical Operating Circuit) in watts,using the following formula:
PDPNP = (maximum wall-cube voltage under load - minimum battery voltage) x (charge current in amps)
6) Limit current into V+ to between 5mA and 20mA. For afixed or narrow-range input voltage, choose R1 in theTypical Operation Circuit using the following formula:
R1 = (minimum wall-cube voltage - 5V)/5mA
7) Choose RSENSE using the following formula:
RSENSE = 0.25V/(IFAST)
8) Consult Tables 2 and 3 to set pin-straps beforeapplying power. For example, to fast charge at arate of C/2, set the timeout to between 1.5x or 2x thecharge period, three or four hours, respectively.
Table 1. Fast-Charge Termination MethodsCharge
RateNiMH Batteries NiCd Batteries
ΔV/Δt and/or temperature, MAX713
ΔV/Δt and temperature,MAX712 or MAX713
> 2C
2C to C/2ΔV/Δt and/or temperature,MAX712 or MAX713
ΔV/Δt and/ortemperature, MAX713
ΔV/Δt and/ortemperature, MAX713
ΔV/Δt and/or temperature, MAX712
< C/2
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Table 2. Programming the Number of Cells
Table 3. Programming the MaximumCharge Time
CONTROL LOGIC
+5V SHUNTREGULATOR
TIMER
PGM2 PGM3
V+
BATT-
BATT-
UNDER_VOLTAGE
BATT-
DRV
V+
REF
100kΩ
100kΩ
N
HOT
ΔV_DETECT
TIMED_OUT
BATT-
FASTCHG
GND
CC
BATT-
GND
CELL_VOLTAGE
INTERNAL IMPEDANCE OF PGM0–PGM3 PINS
FAST_CHARGE
POWER_ON_RESET
IN_REGULATION
VLIMITBATT+
PGM0
PGM1
PGM2
PGM3
PGMx
THITEMP
TLO
ΔVDETECTION
TEMPERATURECOMPARATORS
CURRENTAND
VOLTAGEREGULATOR
COLD
0.4VMAX712MAX713
Figure 1. Block Diagram
PGM1CONNECTION
PGM0CONNECTION
1 V+ V+
NUMBEROF CELLS
2 Open V+
4 BATT- V+
3 REF V+
6 Open Open
5 V+ Open
8 BATT- Open
7 REF Open
10 Open REF
9 V+ REF
12 BATT- REF
11 REF REF
14 Open BATT-
13 V+ BATT-
16 BATT- BATT-
15 REF BATT-
22 V+ REF
PGM3CONN
PGM2 CONN
22 V+ Open
33 V+ BATT-
TIMEOUT(min)
33 V+ V+
45 Open REF
45 Open Open
66 Open BATT-
66 Open V+
90 REF REF
90 REF Open
132 REF BATT-
132 REF V+
180 BATT- REF
180 BATT- Open
264 BATT- BATT-
264 BATT- V+
21
21
21
A/DSAMPLINGINTERVAL
(s) (tA)
21
42
42
42
42
84
84
84
84
168
168
168
168
Enabled
Disabled
Enabled
VOLTAGE-SLOPE
TERMINATION
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
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Detailed DescriptionThe MAX712/MAX713 fast charge NiMH or NiCd batter-ies by forcing a constant current into the battery. TheMAX712/MAX713 are always in one of two states: fastcharge or trickle charge. During fast charge, the current level is high; once full charge is detected, thecurrent reduces to trickle charge. The device monitorsthree variables to determine when the battery reachesfull charge: voltage slope, battery temperature, andcharge time.
Figure 1 shows the block diagram for the MAX712/MAX713. The timer, voltage-slope detection, and temper-ature comparators are used to determine full chargestate. The voltage and current regulator controls outputvoltage and current, and senses battery presence.
Figure 2 shows a typical charging scenario with batteriesalready inserted before power is applied. At time 1, theMAX712/MAX713 draw negligible power from the bat-tery. When power is applied to DC IN (time 2), thepower-on reset circuit (see the POWER
-_ON
-_RESET sig-
nal in Figure 1) holds the MAX712/MAX713 in tricklecharge. Once POWER
-_ON
-_RESET goes high, the device
enters the fast-charge state (time 3) as long as the cellvoltage is above the undervoltage lockout (UVLO) volt-age (0.4V per cell). Fast charging cannot start until (bat-tery voltage)/(number of cells) exceeds 0.4V.
When the cell voltage slope becomes negative, fastcharge is terminated and the MAX712/MAX713 revertto trickle-charge state (time 4). When power is removed(time 5), the device draws negligible current from thebattery.
Figure 3 shows a typical charging event using tempera-ture full-charge detection. In the case shown, the bat-tery pack is too cold for fast charging (for instance,brought in from a cold outside environment). Duringtime 2, the MAX712/MAX713 remain in trickle-chargestate. Once a safe temperature is reached (time 3), fastcharge starts. When the battery temperature exceedsthe limit set by THI, the MAX712/MAX713 revert to trick-le charge (time 4).
0
A
mA
μA
1
0.4
TIME
VOLTAGE
CELL
VOL
TAGE
(V)
CURR
ENT
INTO
CEL
L
CELL
TEM
PERA
TURE
1.4
1.5
1.3
2 4 531. NO POWER TO CHARGER2. CELL VOLTAGE LESS THAN 0.4V3. FAST CHARGE4. TRICKLE CHARGE5. CHARGER POWER REMOVED
TEMPERATURE
Figure 2. Typical Charging Using Voltage Slope
A
mA
μA
1TIME
CELL
TEM
PERA
TURE
CURR
ENT
INTO
CEL
L
TLO
THI
2 431. NO POWER TO CHARGER2. CELL TEMPERATURE TOO LOW3. FAST CHARGE4. TRICKLE CHARGE
Figure 3. Typical Charging Using Temperature
A
1.5
1.4
1.3
mA
μA
1TIME
VREF = VLIMIT
CELL
VOL
TAGE
(V)
CURR
ENT
INTO
CEL
L
2 431. BATTERY NOT INSERTED2. FAST CHARGE3. TRICKLE CHARGE4. BATTERY REMOVED
Figure 4. Typical Charging with Battery Insertion
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The MAX712/MAX713 can be configured so that voltageslope and/or battery temperature detects full charge.
Figure 4 shows a charging event in which a battery isinserted into an already powered-up MAX712/MAX713.During time 1, the charger’s output voltage is regulatedat the number of cells times VLIMIT. Upon insertion ofthe battery (time 2), the MAX712/MAX713 detect cur-rent flow into the battery and switch to fast-chargestate. Once full charge is detected, the device revertsto trickle charge (time 3). If the battery is removed (time4), the MAX712/MAX713 remain in trickle charge andthe output voltage is once again regulated as in time 1.
Powering the MAX712/MAX713AC-to-DC wall-cube adapters typically consist of a trans-former, a full-wave bridge rectifier, and a capacitor.Figures 10–12 show the characteristics of three con-sumer product wall cubes. All three exhibit substantial120Hz output voltage ripple. When choosing an adapterfor use with the MAX712/MAX713, make sure the lowestwall-cube voltage level during fast charge and full load isat least 1.5V higher than the maximum battery voltagewhile being fast charged. Typically, the voltage on the
battery pack is higher during a fast-charge cycle thanwhile in trickle charge or while supplying a load. The volt-age across some battery packs may approach 1.9V/cell.
The 1.5V of overhead is needed to allow for worst-casevoltage drops across the pass transistor (Q1 of Typical
2N3904
D1Q1
V+ DRV
DC IN
R1
R2
MAX712MAX713
Figure 5. DRV Pin Cascode Connection (for high DC IN voltageor to reduce MAX712/MAX713 power dissipation in linear mode)
↑ 1 x
UNDER_VOLTAGE IINN__RREEGGUULLAATTIIOONN
0 x x
↑ x x
PPOOWWEERR__OONN__RREESSEETT
↑ x 1
↑ 0 0
↑ x x
1 0 0
1 0 0
1 0 ↓1 ↓ 0
1 0 0
1 0 0
1 x x
1 x x
1 0 ↑1 ↑ 0
Table 4. MAX712/MAX713 Charge-State Transition Table†
x
CCOOLLDD
x
0
x
1
x
↓1
1
1
↑1
x
0
x
x
x
HHOOTT
x
x
x
1
0
1
1
1
1
1
↑
0
x
x
x
No change
RESULT*
Set trickle
No change
No change
Set fast
No change***
No change
No change
Set fast
Set fast
Set fast**
No change***
Trickle to fast transition inhibited
Trickle to fast transition inhibited
Set trickle
Set trickle
1 x x x ↓ Set trickle
† Only two states exist: fast charge and trickle charge.* Regardless of the status of the other logic lines, a timeout or a voltage-slope detection will set trickle charge.
** If the battery is cold at power-up, the first rising edge on COLD will trigger fast charge; however, a second rising edge will have no effect.
***Batteries that are too hot when inserted (or when circuit is powered up) will not enter fast charge until they cool and power is recycled.
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10 ______________________________________________________________________________________
Operating Circuit), the diode (D1), and the sense resistor (RSENSE). This minimum input voltage require-ment is critical, because violating it can inhibit propertermination of the fast-charge cycle. A safe rule ofthumb is to choose a source that has a minimum inputvoltage = 1.5V + (1.9V x the maximum number of cellsto be charged). When the input voltage at DC IN dropsbelow the 1.5V + (1.9V x number of cells), the partoscillates between fast charge and trickle charge andmight never completely terminate fast-charge.
The MAX712/MAX713 are inactive without the wall cubeattached, drawing 5µA (max) from the battery. DiodeD1 prevents current conduction into the DRV pin. Whenthe wall cube is connected, it charges C1 through R1(see Typical Operating Circuit) or the current-limitingdiode (Figure 19). Once C1 charges to 5V, the internalshunt regulator sinks current to regulate V+ to 5V, andfast charge commences. The MAX712/MAX713 fast
charge until one of the three fast-charge terminatingconditions is triggered.
If DC IN exceeds 20V, add a cascode connection inseries with the DRV pin as shown in Figure 5 to preventexceeding DRV’s absolute maximum ratings.
Select the current-limiting component (R1 or D4) topass at least 5mA at the minimum DC IN voltage (seestep 6 in the Getting Started section). The maximumcurrent into V+ determines power dissipation in theMAX712/MAX713.
maximum current into V+ =
(maximum DC IN voltage - 5V)/R1
power dissipation due to shunt regulator =
5V x (maximum current into V+)
Sink current into the DRV pin also causes power dissipa-tion. Do not allow the total power dissipation to exceedthe specifications shown in the Absolute MaximumRatings.
Fast ChargeThe MAX712/MAX713 enter the fast-charge state underone of the following conditions:
1) Upon application of power (batteries alreadyinstalled), with battery current detection (i.e., GNDvoltage is less than BATT- voltage), and TEMP higher than TLO and less than THI and cell voltagehigher than the UVLO voltage.
2) Upon insertion of a battery, with TEMP higher thanTLO and lower than THI and cell voltage higher thanthe UVLO voltage.
RSENSE sets the fast-charge current into the battery. Infast charge, the voltage difference between the BATT-and GND pins is regulated to 250mV. DRV currentincreases its sink current if this voltage difference fallsbelow 250mV, and decreases its sink current if the volt-age difference exceeds 250mV.
fast-charge current (IFAST) = 0.25V/RSENSE
Trickle ChargeSelecting a fast-charge current (IFAST) of C/2, C, 2C, or4C ensures a C/16 trickle-charge current. Other fast-charge rates can be used, but the trickle-charge current will not be exactly C/16.
The MAX712/MAX713 internally set the trickle-chargecurrent by increasing the current amplifier gain (Figure6), which adjusts the voltage across RSENSE (seeTrickle-Charge VSENSE in the Electrical Characteristicstable).
BATT-
XV+
OPENREF
BATT-
10000
851225612864
CURRENT-SENSE AMPLIFIER
PGM3 FAST_CHARGE Av
1.25V
V+DC IN
GND
DRV
GND
CCBATT-
RSENSE
D1
REF
VLIMIT
CELL_VOLTAGE
BATT-
BATT-
IN_REGULATION
C2
Figure 6. Current and Voltage Regulator (linear mode)
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Nonstandard Trickle-ChargeCurrent Example
Configuration:
Typical Operating Circuit2 x Panasonic P-50AA 500mAh AA NiCd batteriesC/3 fast-charge rate264-minute timeoutNegative voltage-slope cutoff enabledMinimum DC IN voltage of 6V
Settings:
Use MAX713PGM0 = V+, PGM1 = open, PGM2 = BATT-, PGM3 = BATT-, RSENSE = 1.5Ω (fast-charge current, IFAST = 167mA), R1 = (6V - 5V)/5mA = 200Ω
Since PGM3 = BATT-, the voltage on RSENSE is regulat-ed to 31.3mV during trickle charge, and the current is20.7mA. Thus the trickle current is actually C/25, notC/16.
Further Reduction of Trickle-ChargeCurrent for NiMH Batteries
The trickle-charge current can be reduced to less thanC/16 using the circuit in Figure 7. In trickle charge,some of the current will be shunted around the battery,since Q2 is turned on. Select the value of R7 as follows:
R7 = (VBATT + 0.4V)/(lTRlCKLE - IBATT)
where VBATT = battery voltage when chargedITRlCKLE = MAX712/MAX713 trickle-charge current setting
IBATT = desired battery trickle-charge current
Regulation LoopThe regulation loop controls the output voltage betweenthe BATT+ and BATT- terminals and the currentthrough the battery via the voltage between BATT- andGND. The sink current from DRV is reduced when the
output voltage exceeds the number of cells times VLIMIT, or when the battery current exceeds the pro-grammed charging current.
For a linear-mode circuit, this loop provides the followingfunctions:
1) When the charger is powered, the battery can beremoved without interrupting power to the load.
2) If the load is connected as shown in the TypicalOperating Circuit, the battery current is regulatedregardless of the load current (provided the inputpower source can supply both).
Voltage LoopThe voltage loop sets the maximum output voltagebetween BATT+ and BATT-. If VLIMIT is set to less than2.5V, then:
Maximum BATT+ voltage (referred to BATT-) = VLIMIT x(number of cells as determined by PGM0, PGM1)
VLIMIT should be set between 1.9V and 2.5V. If VLIMITis set below the maximum cell voltage, proper termination of the fast-charge cycle might not occur.Cell voltage can approach 1.9V/cell, under fast charge,in some battery packs. Tie VLIMIT to VREF for normaloperation.
With the battery removed, the MAX712/MAX713 do notprovide constant current; they regulate BATT+ to themaximum voltage as determined above.
OPEN 2C IFAST/32
FAST-CHARGERATE
TRICKLE-CHARGECURRENT (ITRICKLE)
V+ 4C IFAST/64
BATT- C/2 IFAST/8
PGM3
REF C IFAST/16
Table 5. Trickle-Charge CurrentDetermination from PGM3
FASTCHG
RSENSE
BATTERY
R7
Q2
10k
V+
10k
DRV
D1Q1DC IN
GND
MAX712MAX713
Figure 7. Reduction of Trickle Current for NiMH Batteries (Linear Mode)
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The voltage loop is stabilized by the output filter capacitor. A large filter capacitor is required only if theload is going to be supplied by the MAX712/MAX713 inthe absence of a battery. In this case, set COUT as:
COUT (in farads) = (50 x ILOAD)/(VOUT x BWVRL)
where BWVRL = loop bandwidth in Hz(10,000 recommended)
COUT > 10µF
ILOAD = external load current in amps
VOUT = programmed output voltage(VLIMIT x number of cells)
Current Loop Figure 6 shows the current-regulation loop for a linear-mode circuit. To ensure loop stability, make sure thatthe bandwidth of the current regulation loop (BWCRL) islower than the pole frequency of transistor Q1 (fB). SetBWCRL by selecting C2.
BWCRL in Hz = gm/C2, C2 in farads,gm = 0.0018 Siemens
The pole frequency of the PNP pass transistor, Q1, canbe determined by assuming a single-pole current gainresponse. Both fT and Bo should be specified on thedata sheet for the particular transistor used for Q1.
fB in Hz = fT/Bo, fT in Hz, Bo = DC current gain
Condition for Stability of Current-Regulation Loop:
BWCRL < fBThe MAX712/MAX713 dissipate power due to the cur-rent-voltage product at DRV. Do not allow the powerdissipation to exceed the specifications shown in theAbsolute Maximum Ratings. DRV power dissipation canbe reduced by using the cascode connection shown inFigure 5.
Power dissipation due to DRV sink current =(current into DRV) x (voltage on DRV)
Voltage-Slope CutoffThe MAX712/MAX713’s internal analog-to-digital con-verter has 2.5mV of resolution. It determines if the bat-tery voltage is rising, fal l ing, or unchanging bycomparing the battery’s voltage at two different times.After power-up, a time interval of tA ranging from 21secto 168sec passes (see Table 3 and Figure 8), then abattery voltage measurement is taken. It takes 5ms toperform a measurement. After the first measurement iscomplete, another tA interval passes, and then a second measurement is taken. The two measurementsare compared, and a decision whether to terminatecharge is made. If charge is not terminated, another fulltwo-measurement cycle is repeated until charge is
terminated. Note that each cycle has two tA intervalsand two voltage measurements.
The MAX712 terminates fast charge when a compari-son shows that the battery voltage is unchanging. TheMAX713 terminates when a conversion shows the bat-tery voltage has fallen by at least 2.5mV per cell. This isthe only difference between the MAX712 and MAX713.
Temperature Charge CutoffFigure 9a shows how the MAX712/MAX713 detect over-and under-temperature battery conditions using negativetemperature coefficient thermistors. Use the same modelthermistor for T1 and T2 so that both have the samenominal resistance. The voltage at TEMP is 1V (referredto BATT-) when the battery is at ambient temperature.
The threshold chosen for THI sets the point at whichfast charging terminates. As soon as the voltage-onTEMP rises above THI, fast charge ends, and does notrestart after TEMP falls below THI.
The threshold chosen for TLO determines the tem-perature below which fast charging will be inhibited. If TLO > TEMP when the MAX712/MAX713 start up, fastcharge will not start until TLO goes below TEMP.
The cold temperature charge inhibition can be disabledby removing R5, T3, and the 0.022μF capacitor; and bytying TLO to BATT-.
To disable the entire temperature comparator charge-cutoff mechanism, remove T1, T2, T3, R3, R4, and R5,and their associated capacitors, and connect THI to V+and TLO to BATT-. Also, place a 68kQ resistor fromREF to TEMP, and a 22kΩ resistor from BATT- to TEMP.
5ms
5ms
5ms
5ms
5ms
5mstA tA tA tA tA tA
INTERVAL
NOTE: SLOPE PROPORTIONAL TO VBATT
INTERVAL INTERVAL INTERVAL INTERVAL INTERVAL
NEGATIVERESIDUAL
POSITIVE RESIDUAL
ZERORESIDUAL
VOLTAGERISES
0 t
ZEROVOLTAGE
SLOPECUTOFF FOR MAX712
NEGATIVEVOLTAGE
SLOPECUTOFF FOR MAX712
OR MAX713COUN
TS
Figure 8. Voltage Slope Detection
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Some battery packs come with a temperature-detect-ing thermistor connected to the battery pack’s negative terminal. In this case, use the configuration shown inFigure 9b. Thermistors T2 and T3 can be replaced bystandard resistors if absolute temperature charge cut-off is acceptable. All resistance values in Figures 9aand 9b should be chosen in the 10kΩ to 500kΩ range.
__________Applications InformationBattery-Charging Examples
Figures 13 and 14 show the results of charging 3 AA,1000mAh, NiMH batteries from Gold Peak (part no.GP1000AAH, GP Batteries (619) 438-2202) at a 1A rateusing the MAX712 and MAX713, respectively. The Typical Operating Circuit is used with Figure 9a’s thermistor configuration .
DC IN = Sony AC-190 +9VDC at 800mA AC-DC adapterPGM0 = V+, PGM1 = REF, PGM2 = REF, PGM3 = REF R1 = 200Ω, R2 = 150Ω, RSENSE = 0.25ΩC1 = 1µF, C2 = 0.01µF, C3 = 10µF, VLIMIT = REF R3 = 10kΩ, R4 = 15kΩT1, T2 = part #14A1002 (Alpha Sensors: 858-549-4660) R5omitted, T3 omitted, TLO = BATT-
0.022μF
0.022μF
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BEREPLACED BY STANDARD RESISTORS.
1μF
TEMP
TLO
IN THERMALCONTACT WITH
BATTERY
AMBIENTTEMPERATURE
AMBIENTTEMPERATURE
T3
+2.0V
T2
T1R3
R4
R5
HOT
REF
THI
BATT-
COLD
MAX712MAX713
Figure 9a. Temperature Comparators
MAX712MAX713
0.022μF0.022μF
NOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 CAN BEREPLACED BY STANDARD RESISTORS.
1μFTEMP
TLO
AMBIENTTEMPERATURE
AMBIENTTEMPERATURE
IN THERMALCONTACT WITH
BATTERY
T3
+2.0V
T1
T2
R4
R3R5HOT
REF
THI
BATT-
COLD
Figure 9b. Alternative Temperature Comparator Configuration
11
60 200 600 1000
7
10
MAX
712/
713
OUTP
UT V
OLTA
GE (V
)
400 800
9
8 120Hz RIPPLE
LOW PEAK
HIGH PEAK
LOAD CURRENT (mA)
Figure 10. Sony Radio AC Adapter AC-190 Load Characteristic,9VDC 800mA
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Linear-Mode, High Series Cell CountThe absolute maximum voltage rating for the BATT+ pinis higher when the MAX712/MAX713 are powered on. Ifmore than 11 cells are used in the battery, the BATT+input voltage must be limited by external circuitry whenDC IN is not applied (Figure 15).
Efficiency During DischargeThe current-sense resistor, RSENSE, causes a small efficiency loss during battery use. The efficiency loss issignificant only if RSENSE is much greater than the
battery stack’s internal resistance. The circuit in Figure16 can be used to shunt the sense resistor wheneverpower is removed from the charger.
Status OutputsFigure 17 shows a circuit that can be used to indicatecharger status with logic levels. Figure 18 shows a circuit that can be used to drive LEDs for power andcharger status.
11
6
50 200 600 1000
7
10
MAX
712/
713
OUTP
UT V
OLTA
GE (V
)
400 800
9
8
LOW PEAK
HIGH PEAK
120Hz RIPPLE
LOAD CURRENT (mA)
Figure 11. Sony CD Player AC Adapter AC-96N LoadCharacteristic, 9VDC 600mA
4.3
4.20 30 90
4.5
5.0
4.9
4.7
4.4
BATT
ERY
VOLT
AGE
(V)
BATT
ERY
TEM
PERA
TURE
(°C)
60TIME (MINUTES)
4.8
4.6
ΔVΔt CUTOFF
26
24
30
40
38
34
28
36
32V
T
MAX712/713
Figure 13. 3 NiMH Cells Charged with MAX712
10
80 200 600
12
18
MAX
712/
713
OUTP
UT V
OLTA
GE (V
)
400LOAD CURRENT (mA)
800
16
14HIGH PEAK
LOW PEAK
120Hz RIPPLE
Figure 12. Panasonic Modem AC Adapter KX-A11 LoadCharacteristic, 12VDC 500mA
4.3
4.20 30 90
4.5
5.0
4.9
4.7
4.4
MAX712/713
BATT
ERY
VOLT
AGE
(V)
BATT
ERY
TEM
PERA
TURE
(°C)
60TIME (MINUTES)
4.8
4.6
26
24
30
40
38
34
28
36
32
ΔVΔt CUTOFF
V
T
Figure 14. NiMH Cells Charged with MAX713
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Q1 D1
R2150Ω
DC IN
33kΩ
Q2
500Ω
DRV
BATT+
TO BATTERY POSITIVE TERMINAL
MAX712MAX713
Figure 15. Cascoding to Accommodate High Cell Counts forLinear-Mode Circuits
100kΩ
D1
V+
GND
RSENSE
>4 CELLS
LOW RONLOGIC LEVELN-CHANNELPOWERMOSFET
*
*
MAX712MAX713
100kΩ
Figure 16. Shunting RSENSE for Efficiency Improvement
VCC
OV = NO POWER5V = POWER
OV = FASTVCC = TRICKLE OR NO POWER
MAX712MAX713
V+
FASTCHG
10kΩ
Figure 17. Logic-Level Status Outputs
V+
R1
470ΩMIN
FASTCHG
DC IN
CHARGE POWER
FAST CHARGE
MAX712MAX713
Figure 18. LED Connection for Status Outputs
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16 ______________________________________________________________________________________
Ordering Information (continued) ___________________Chip Topography
DRV
THI
TLO
PGM3
0.126(3.200mm)
0.80"(2.032mm)
TEMP FASTCHG PGM2
GND
BATT-
CC
BATT+ VLIMIT REF V+
PGM1
PGM0
TRANSISTOR COUNT: 2193
SUBSTRATE CONNECTED TO V+
*Contact factory for dice specifications.**Contact factory for availability and processing to MIL-STD-883.
PART TEMP RANGE PIN-PACKAGE
MAX713CPE 0°C to +70°C 16 Plastic DIP
16 Narrow SO0°C to +70°CMAX713CSE
MAX713C/D 0°C to +70°C Dice*
16 Plastic DIP-40°C to +85°CMAX713EPE
MAX713ESE
MAX713MJE
-40°C to +85°C
-55°C to +125°C
16 Narrow SO
16 CERDIP**
Package Information(For the latest package outline information and land patterns,go to www.maxim-ic.com/packages.)
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
16 Plastic DIP P16-1 21-0043
16 Narrow SO S16-1 21-0041
16 CERDIP J16-3 21-0045
NiCd/NiMH BatteryFast-Charge Controllers
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Revision History
REVISIONNUMBER
REVISIONDATE
DESCRIPTIONPAGES
CHANGED
6 12/08Removed switch mode power control and added missing packageinformation
1, 5, 6, 9, 10, 12,13, 14, 16, 17
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